1. Field of the Invention
The subject invention relates to RF power suppliers used in plasma chambers and, more specifically, RF power suppliers enabling application of multiple-frequency RF power.
2. Related Art
Plasma chambers utilizing dual RF frequencies are known in the art. Generally, a plasma chamber of dual frequencies receive RF bias power having frequency below about 15 MHz, and an RF source power at higher frequency, normally 40-200 MHz. In this context, RF bias refers to the RF power which is used to control the ion energy and ion energy distribution. On the other hand, RF source refers to RF power which is used to control the plasma ion dissociation or plasma density. For some specific examples, it has been known to operate etch plasma chambers at, e.g., bias of 2 MHz or 13 MHz, and source at 27 MHz, 60 MHz, 100 MHz, and higher.
Recently it has been proposed to operate a plasma chamber at one bias frequency and two source frequencies. For example, it has been proposed to operate a plasma etch chamber at bias frequency of 2 MHz and two source frequencies of 27 MHz and 60 MHz. In this manner, the dissociation of various ion species can be controlled using the two source RF frequencies. Regardless of the configurations, in the prior art each frequency is provided by an individual RF power supplier. For further information, the reader is directed to U.S. Pat. Nos. 6,281,469 and 7,144,521, and to U.S. Publication 2005/0264218.